This invention relates to sewing machines and particularly to an improved workpiece feeding mechanism of the type that imparts feeding action to both the top and bottom surfaces of the workpiece in timed relationship with the stitch forming mechanism.
For sewing operations involving fabrics, such as denim used in jeans that are difficult to feed and operations where the control of the fabrics layers relative to each other is critical, feeding devices that impart a feeding action to both the upper and lower surface of the workpiece are used. The drive mechanism for the upper surface feeder is a critical element of such a system. The upper surface feeder must be synchronized with the lower surface feeder and with the needle drive and must be intermittent so that movement to the fabric is imparted only when the needle is not penetrating the fabric. Another consideration that is important with respect to the upper surface feeder is that the operators view of the work area cannot be overly restricted. Operators of commercial sewing machines of this type spend long periods of time working at the machine and it is very important that their working conditions are favorable and will not cause undue fatigue. For this reason the feeding devices for imparting movement to the workpiece should be free of vibrations and have a tolerable noise level. The drive mechanism for the upper surface feeder cooperates with the conventional lower surface feed dog mechanism that is disposed beneath the presser mechanism.
A Union Special Corporation, class 35800 sewing machine includes mechanism for imparting a feeding action to both the upper and lower surfaces of the workpiece. In this machine the drive for the upper mechanism is derived from the main drive shaft through an eccentric and pitman that oscillates a bellcrank which is connected to an input clutch drive member through a connecting bar. The clutch imparts a drive motion, in one direction, to the drive mechanism for the upper surface feeder. This commercially available machine feeds fabric that is difficult to control and maintains accurate alignment of the layers of material, however the eccentric drive taken from the main drive shaft produces considerable vibrations and sound levels. The vibrations and sound level produced by the workpiece feeding mechanism of this machine, while tolerable, can be improved which not only improves the operator's working environment but also results in a more durable machine and a machine that requires less service. By eliminating the eccentric and pitman drive from the main shaft and replacing it with a belt drive the vibration level is greatly reduced, the lubrication task simplified and the durability of the machine is improved. The level of vibrations and sound that is present in the prior art machines is particularly undesirable in commercial sewing operations where poor working environment will reduce the time period that a machine operator can be productive at his or her work station. The reduction of vibrations and sounds, that are unpleasant to the sewing machine operator and adversely effect output, constitutes a very important and significant improvement to machines of this type. The constant vibrations produced by the prior art device also limits the devices useful life and has adverse effects on other components of the sewing machine. For the foregoing reasons, there is a need for a drive mechanism for the upper surface feeder of a machine of this type that will not produce undesirable vibrations and sounds.